Method of improving smoke filter

ABSTRACT

A method of increasing the smoke filtering activity of porous glass which involves the incorporation of hydroxyl ions in high concentrations in the pores of the microporous glass article. The microporous glass is heated at a temperature in the order of 100* to 600*C for about 5 to 120 minutes in an atmosphere of water and an inert gas.

United States Patent 1191 Hammel et al.

METHOD OF IMPROVING SMOKE FILTER Inventors: Joseph J. Hammel, Pittsburgh, Pa.;

3 John D. MacKenzie, Los Angeles,

Calif.

Assigneei PPG Industries, Inc., Pittsburgh, Pa.'

Filed: Apr. 15, 1971 Appl. No.: 134,158

Related U.s. Application Data Division of Ser. No. 822,213 May 6, 1969, Pat. No.

3,602,233, which is a continuation-in-part of Ser. No. 736,670, June 13, 1968, abandoned.

US. Cl 117/106 R, 117/100 S, 117/124 A, 117/126 GF, 131/10 R Int. Cl 844d l/02 Field of Search" 117/100 S, 119, 113, 126 GF,

117/126 GM, 16, 118, 106 R, 124 A, 98;

References Cited UNITED STATES PATENTS ll/1962 Marzocchi 117/54 1 Feb. 19, 1974.

Hood /22 2/1938 3,075,494 l/l963 Toulniin, Jr. ll7/98 3,275,470 9/l966 Charles 117/124 A Primary Examiner-William D. Martin Assista nt Examiner-Dennis C. Konopacki Attorney, Agent, or Firm-William J. Uhl; John E.

Curley [5 7 ABSTRACT A method of increasing the smoke filtering activity of porous glass which involves the incorporation of hydroxyl ions in high concentrations in the pores of the microporous glass article. The microporous glass is heated at a temperature in the order of to 600C for about 5 to 120 minutes in an atmosphere of water and an inert gas. 1

4 Claims, 5 Drawing Figures 1 METHOD OF IMPROVING SMOKE FILTER RELATED APPLICATIONS This application is a division of copending application Ser. No. 822,213, filed May 6, 1969, now US. Pat. No. 3,602,233, which application is a continuation-inpart of application Ser. No. 736,670, filed June 13, 1968, now abandoned.

BACKGROUND OF THE INVENTION As is well known, unfiltered tobacco smoke carries with it nicotine, various tar-like pyrogenic substances, and toxic gases. In smoking tobacco, whether as a cigarette, cigar, or pipe, if not removed these harmfulingredients are absorbed by mucosa of the smoker and, when inhaled, they travel further into the lungs where they exert a highly-irritating action.

Cigarette manufacturers are ever endeavoring to find a means which will remove these irritating substances as much as possible from tobacco smoke. Filtering and- /or absorbent means built into the cigarette, cigarette holder, or pipe have been extensively manufactured and sold with claims that ahigh percentage of the tarlike pyrogenic substances and toxic gases harmful to the human being are removed from the smoke before entering the mouth of the smoker.

The filters and/or absorbents are usually in the form of a case-capsule, shell, or the like, which has in it the filter and/or absorbent materials. They are sometimes called cartridges. The cartridges are used in pipes and cigarette holders until ren'ewal is necessary. Then the old cartridge is replaced by anew one. With cigarettes, the cartridge or container is built in the mouth end of the cigarette and is thrown away when the cigarette has been smoked. Thus, those used as a part of the cigarette are sometimes called throw away filters.

Many substances have been, and continue to be, employed or are known, which serve as filters and/or absorbents in cigarettes, pipes, or cigarette holders. Raw cotton, ground cork, carbonized tobacco, wool, asbestos, ion exchange resins, and charcoal are examples. Other known filters and/or absorbents for the tar-like and other impurities Carried by tobacco smoke are I small pellets of silica gel and clays. Also, cigarettes per se are ,used in pipes as the filtering and/or absorbent material for the tobacco smoke.

It is desired in a tobacco smoke filter that the harmful ingredients be removed without removing the taste of the tobacco smoke. It is also desired that the filter not be so efficient as to quickly clog up and prevent pas sage of the smoke altogether. It is important that a comfortable level of draw be maintained throughout the smoke. The filter material must be of such material that the harmful ingredients that are filtered out initially are not subsequently released upon the passage of further smoke through the filter. In addition to all these considerations, it is most desirable that the filter be inexpensive.

INVENTION skeletal structure having a low borate content. Suitable microporous glass can be produced according to the teachings of U. S. Pat. No. 2,106,744 wherein it is disclosed that an alkali borosilicate glass is heat treated to develop two separate glassy phases, one of which can be leached out by acid treating thereby leaving a highly-porous glass structure. This method of leaching glass is well known in the art and, other than setting forth a specific example of the leachinglmethod to illustrate a preferred mode of carrying out the invention, the description of the invention will not dwell on the leaching technology.

Glasses useful in this invention are glasses which may be phase separated to produce an article having a continuous, leachable, minor phase such as the borate phase in a phase-separatedborosilicate glass. It is significant in this invention that the base glass be phaseseparable and leachable to produce a microporous structure having interconnecting pores. Microporous structures of this kind are, most easily obtained from glasses having a major phase substantially of silica inasmuch as silica is substantially more acid resistant than other glassy phases such as borates, phosphates, and the like. A major phasesubstantially of alumina is also useful, but base glasses having a high alumina content are difficult to melt and frequently have a tendency to crystallize rather than separate into two glassy phases.

The microporous glasses of thisinvention are skeletal glassy structures preferably high in silica, e.g., greater than about 90 percent by weightiof SiO Base glasses amenable to phase separation and leaching to form such microporous structures include metal borosilicates, especially alkali metal borosilicates, alkaline earth borosilicates, and metal borosilicates such as lead borosilicate, zinc borosilicate, titanium borosilicate, and the like. In the borosilica glasses, the weight ratio of SiO to B 0 will be significantly greater than l:l so that upon phase separation the major phase will be the silicate phase which will contain only minor quantities of metal, e.g., Na O, BaO PhD, and the like, and other glass formers such as B 0 A1 0 P 0 and the like. Especially useful are alkali metal borosilicate glasses containing less than about 15 percent by weight of alkali metal, less than about 50 percent by weight of boron oxide, and greater than about percent by weight of silica. A preferable compositional range is about 5 to 10 percent by weight of alkali metal, about 15 to 30 percent by weight of B 0 and about to percent by weight of SiO Small quantities of other glass formers, fluxes, and other oxides, halides, nitrides, and the like may be included in the base glass composition so long as the quantities of such ingredients do not alter the phase separation and leaching characteristics of the glass.

The original composition of the glass is important only to the extent that it can be phase separated and leached to a microporous structure having interconnecting pores. While the metal borosilicate glasses are preferred because of their facility of readily phase separating and ease of leaching, other glasses such as soda-lime-silica, germanate, and commercial fiber glass compositions are useful to the extent that they can be phase separated into two glassy phases-a minor phase readily leached by acids and a major phase substantially insoluble in acids other than hydrofluoric acid or at least substantially insoluble in those acids which readily dissolve the minor glassy phase. Also, the minor phase should be substantially continuous so that the resulting porous glass structure contains pores which are interconnecting.

Phase-separable glasses useful in this invention may be phase separated by heating at elevated temperatures below the miscibility temperature although some glasses such as the lithia borosilicate glasses tend to phase separate upon cooling from melting temperatures. A preferred manner of phase separating glasses such as metal borosilicates, especially alkali metal silicates, is by heating said glasses to about 450C. to about 700C. or higher but below the miscibility temperature of the glass for a sufficient period of time to form a major silica-rich phase and a minor, substantially continuous borate-rich phase.

Leaching of phase-separated glasses described above may be accomplished in acids such as hydrochloric, sulfuric, nitric, and the like, which dissolve the acidsoluble minor phase, e.g.', borate-rich phase, to leave a skeletal glass structure of inter-connecting micropores. The leaching is preferably accomplished at temperatures above room temperature and through use of concentrated acids. Leaching proceeds rapidly at temperatures between about 70C. and 200C. Concentration of the acid should be at least 1N and, preferably, about 3N.

The leached glasses useful in this invention have an approximate pore volume of about 5 to 70 percent, preferably about to 50 percent. The pores are interconnecting and the average size of the pore openings ranges from about 5 to 10,000 angstroms in diameter, with pore openings of about 10 to 1,000 angstroms readily obtained in variations in techniques of phase separation and leaching. Microporous glass having pore openings of about 40 to 1,000 angstroms has proved to be especially effective in removing noxious gases and particulate matter from tobacco smoke.

The porous glass of this invention has a nitrogen surface area on the order of about 50 to 500 square meters per gram. Porous glass of surface areas about 50 to 200 square meters per gram are readily obtainable in a very economical manner and provide efficient tobacco smoke filters. A relatively-high concentration of hydroxyl groups exists on the surface of the pores and these hydroxyl groups readily form hydrogen bonds with molecules coming in contact with the surface. The number of hydroxyl groups present can be increased by treatment with water vapor.

After phase separation and leaching, the skeletal glass structure is substantially SiO with a minor quantity of other glass formers and flux present. Microporous glasses derived from metal borosilicates, for example, alkali borosilicates, contain greater than 90 percent by weight SiO less than-about 8 percent by weight B 0 and less'than 2 percent by weight alkali metal oxide.

In a preferred mode of the invention, the phaseseparated glass is crushed, sieved, and leached so that it can be used in granular form. In order to prevent a large pressure drop (difficult or uncomfortable draw), the particle size is in the range of l to 1,000 microns, preferably 100 to 500 microns. Alternatively, the glass can be leached first and then crushed to the desired particle size.

The microporous glass can also be used in bulk and in fibrous form. Microporous glass granules or fibers can be combined with the tobacco fibers and/or they can be incorporated in a filter-tip cartridge at one end of the cigarette or cigar. When combined with the tobacco, the microporous glass can comprise 1 to 50 percent, preferably 5 to 20 percent, by weight of the microporous glass and tobacco. Glass fibers can serve the additional function of holding the tobacco ash together since they are incombustible. The strength of thefine glass fibers, 0.5 to 20 microns inv diameter, is not sufficient, however, to prevent the ash from being dislodged upon being tapped in the normal smoker s manner. The length of the fibers can vary from :4; to 3 inches, depending upon the desire .of having the fibers hold the ash together. The longer the fiber, the better such purpose is served. 1

The microporous glass is also used in cartridge form in a cigarette or cigar holder and in a pipe filter.

The microporous glass fibers can also be used in bulk or paper form to serve as a filter. For example, a combination of cellulose fibers and glass fibers readily form a paper which can be used as a filter medium. Very fine glass fibers, on the order of 0.5 to 5 microns, are readily formed into a glass paper. The porous glass can also be used in combination with one or more other filter materials such -as charcoal and those mentioned above.

Fibers of microporous glass having inter-connecting pores have been found to be an especially effective multipurpose tobacco filter. Fibers of microporous glass can be formed in a tow and utilized in a manner similar to commercial cellulose acetate fibers. In cigarettes, a filter comprised solely of fiber glass can be readily formed by current filter-forming equipment. The fibers are thus more easily fabricated than granular materials such as granular microporous glass or charcoal which require a complete enclosure to contain these materials.

Fibers of microporous glass useful in this invention generally have a diameter of about 0.5 to about 20 microns or more. Diameters greater than 20 microns effectively filter gases and particulate matter from tobacco smoke but are more difficult to fiberize. A 20 millimeter length of a microporous fiber glass filter attached to a commercial brand cigarette was found to be about 50 percent more effective than a commercial cellulose acetate filter of comparable draw in removing particulate matter and gases.

Fibers of microporous glass may be readily obtained by melting and drawing phase-separable glass compositions according to conventional fiber glass techniques. After fibers of microporous glass are drawn, they are phase separated and leached according to the techniques described hereinabove. Sizing of the glass fibers to desired lengths may be accomplished at any time after drawing.

The microporous glass filter activity is improved by increasing the concentration of hydroxyl groups on the surfaces of the pores. This is accomplished by heating the microporous glass, in bulk, granular, or fibrous form, at an elevated temperature, i.e., on the order of to 600C, preferably about 450 to 550C. in an atmosphere consisting essentially of H 0 and an inert gas. A suitable atmosphere contains 10 to 90 percent by volume of H 0 vapor and 10 to 90 percent N gas. This treatment is continued for a period of about 5 to minutes with a longer time being required for a lower treatment temperature.

The activity of the porous glass surfaces can be altered by incorporating transition metal ions into or on the surface of the glass. This can be done by ion exchange at elevated temperatures or immersion in a metal ion solution at low temperatures and subsequently heating the coated surfaces at elevated temperatures, i.e., 100 to 600C., preferably 450 to 550C.

The invention and its uses are described in further detail in the examples and in conjunction with the drawing in which:

FIG. 1 is a view, partly in section, of a cigarette illustrating the use of the filter medium;

FIG. 2 is a view, partly in section, of a cigarette illustrating another embodiment of the invention;

FIG. 3 is a view, partly in section, of a cigarette illustrating a further embodiment of the invention;

FIG. 4 is a view, partly in section, illustrating the use of the invention in a cigarette holder;

FIG. 5 is a view, partly in section, illustrating the use of the invention in a pipe; and

FIG. 6 is a micrograph of the surface of a porous glass article having inter-connecting micropores.

In FIG. 1 of the drawing there is shown a cigarette 10 containing tobacco ll enclosed in cigarette paper 12. Granules 14 of a leached alkali borosilicate glass are enclosed in a container at the smokers end of the cigarette 10. The granules 14 are prepared and treated as described hereinafter in the examples. The container 15 can be made of paper or plastic according to conventional cigarette manufacturing techniques. Substitution of microporous glass fibers for granules in this article would result in a similar construction but without requiring a container for the filter media, i.e., a structure substantially identical to a commercial cellulose acetate filter cigarette would result.

In FIG. 2 of the drawing there is shown a cigarette constructed of cigarette paper 12 containing tobacco 11 having intermingled therewith leached porous alkali borosilicate glass fibers 21. Filter granules 14 are enclosed in container 15 and are inserted at the smokers end of the cigarette 20 as in FIG. 1.

In FIG. 3 of the drawing there is shown a cigarette 30 similar to cigarette 10 but with a different filter medium enclosed in container 15. The filter medium is composed of three sections. The section next to the tobacco 11 is made of paper 32 composed of leached alkali borosilicate fibers and cellulose fibers. The intermediate section is composed of granules 14. The section next to the smoker is composed of conventional cellulose paper 31 used commercially in cigarettes such as the Tareyton or Lark filter cigarette.

In FIG. 4 there is shown a cigarette holder 40 containing in the removable mouthpiece 41 a filter medium composed of granules 14 enclosed in container 15.

In FIG. 5 there is shown a pipe 50 having in the removable mouthpiece 51 a filter medium composed of granules 14 enclosed in container 15.

FIG. 6 is an electron micrograph of 150,000X magnification showing the size and inter-connecting nature of the micropores. The microporous glass shown here was produced from the composition and in the manner described in Example 1. The width of the micrograph represents one micron width of material. The dark portions in the micrograph are the pores which can be directly measured from themicrograph. The pores shown in FIG. 1 have an average diameter of about 70 angstroms.

The manufacture and testing of the best known modes contemplated for filter media of the present invention are described in the following examples.

EXAMPLE I An alkali borosilicate glass composed in weight per cent of 5 percent Na O, 20 percent B 0 and percent SiO is prepared by conventional sheet glass making techniques. The glass is heated at 1,1 10F. for 2 hours to develop two separate glassy phases. The glass is then crushed into small particles and sieved to retain particles 300 to 400 microns in size. These particles are immersed for 1 hour in an acid bath comprising 3N hydrochloric acid at 98C. This leaches out the more soluble glassy phase, leaving a porous glassy matrix. After the acid treatment, the porous glass matrix is washed with water to remove all traces of the soluble phase and any soluble impurities such as iron, which may have been acted on by the acid. This washing is done in running water for a period of one hour. The porous glass granules had pores ranging in size from 50 to 100 angstroms.

The leached porous glass has a chemical analysis of 96 percent SiO 0.5 percent Na O and 3.5 percent B 0 The leached granules are then heat treated for 30 minutes at 500C. in an atmosphere composed of percent'by volume water vapor and 20 percent by volume nitrogen. This treatment approximately doubles concentration of hydroxyl groups on the surfaces of the pores in the granules.

The granules as thus prepared are tested in various ways to determine their filtering effectiveness as compared with present commercial cigarette filters. The filters are tested in asmoking machine which exerts puffs of 2 second duration at intervals of 60 seconds with an average pressure drop of about 12 centimeters of water on each puff. Each test is carried out for a series of 9 puffs.

A filter holder with a volume of 0.22 cubic centimeters is inserted in the smoking apparatus. The porous glass granules are tested in comparison with activated charcoal presently used in commercially available filter cigarettes. The filter holder contains about 0.16 grams of porous glass granules or 0.13 grams of granular activated charcoal. The filter is made up of three segments as shown in FIG. 3 of the drawing with the intermediate section being the filter holder as just described and the outer sections both being of cellulose paper. Each section is about 20 millimeters in length.

The average of a greater number of tests of weight gain per test is shown below:

Filter Weight Gains Filter (Milligrams) l. Cellulose plus activated charcoal 18.7 2. Cellulose plus porous glass 20.6 3. Cellulose (all three sections) 11.9

tracted material, whereas the tars represent approximately per cent by weight of the material. Infrared spectra of the extract from the porous glass granules reveals a very complex mixture which is about 90 percent by weight aromatic and cyclic compounds and about 10 percent by weight humectant. Visually the charcoal extract is light brown and oily, whereas the porous glass extract is dark brown and highly viscous. The extract from the cellulose in all three filters is approximately 50 per cent tars and 50 per cent humectant materials and is dark and oily (only slightly viscous).

The above test was conducted on a Lark cigarette wherein porous glass and cellulose were substituted for charcoal in the three-part filter.

The highly volatile gases which pass through the filters in the above tests are collected in a cold trap and analyzed. The cellulose-porous glass gaseous test samples show lower amounts of HCN, CH and disubstituted ring compounds than the cellulose gaseous test samples. 1 1

Taste tests and draw tests of the three types of filters do not show a significant difference in taste or draw from various commercially used cigarette tobacco.

EXAMPLE ll Lithia-Containing Porous Glass Materials A lithia borosilicate glass of the following calculated composition was prepared:

U 0 3 per cent by weight B 0 20 per cent by weight SiO 77 per cent by weight U 0 1 per cent by weight Na O 4 per cent by weight B 0 20 per cent by weight SiO 75 per cent by weight Lithium carbonate, sodium carbonate, boric acid, and silica were admixed and melted at about 1,450C.

The glass was cooled by quenching in a container of water, which also caused fritting of the glass; that is,- small particles of the glass are obtained in this manner. Phase separation was accomplished by heat treating the glass at about 600C. for 4 hours. The heat-treated material was transparent and exhibited only slight opalescence, indicating that the borate phase was present in very fine veins; that is, about 50 to 100 angstroms in diameter. Y

The glass was sieved and crushed to obtain a grain size of about 0.3 to about 0.7 millimeters. The fine particles were leached in three normal hydrochloric acid for 8 hours at 98C. An electromicrograph of the porous material indicated pore size'range of about 75 angstroms to about 150 angstroms.

EXAMPLE III Various Pore-Sized Material A porous material was prepared by various heat treatments from a soda borosilicate glass having the following calculated composition:

Na O 5 per cent by weight B 0; 20 per cent by weight SiO per cent by weight The glass was melted at 1,450C. and fritted by quenching in water. The glass was crushed and sieved to obtain grain sizes of between'0.3 and 0.7 millimeters. The glass was divided into several portions which were heat treated for various periods of time to promote variations in phase separation. All the following glasses were leached in three normal hydrochloric acid for 8 hours at 98C. and washed thoroughly. The pore size of the various glasses was determined by measuring the leached areas on an electron micrograph. This measurement has an accuracy of about :25 per cent although the measurement gets more accurate as the pores get larger.

Glass la This glass was heat treated for 1 hour at 630C. The pore size was determined to be about 100 angstroms on the average.

Glass lde This material was heat treated for 3 5% hours at 630C. The pore size hadan average diameter of 250 angstroms.

Glass 1e This material was heat treated for 3 hours at 630C. and had an average pore sizeof 250 angstroms.

Glass If This glass was heat treated for 16 hours at 760C. and had an average pore size of between about 750 and 1,000 angstroms.

Glass lg This glass was heat treated 3 hours at 675C. and had an average pore size of about 500 angstroms.

The effectiveness of the above porous glasses having a range of pore sizes as cigarette or tobacco smoke filters was tested in the following manner:

Particulate Matter Filtration 1 the Winston cigarette with the following lengths of maminute.

Average Filter Disc Weight Sample Gain (MGS) Winston cigarette control 21.0 Glass lde 22.6 Glass 1] 22.8 Glass lg 2l.l

The average filter disc weight gain is the particulate matter collected on a Cambridge filter which filters out 20 the particulate matter which passes through the cigarette filter. It is readily seen that the above filters are about as effective as the cellulose filter in removing particulate matter. The Glass lg filter having a pore size of about 500 angstroms appears slightly more effective than the porous filters having pore sizes of 250 angstroms or in the 750 to 1,000 angstrom range.

Gas Filter Effectiveness The above porous glasses were tested for their effec- 30 tiveness in removing acetaldehyde and acetone. The test was conducted in a similar manner to that for the particulate filtration test with a Winston cigarette with a cellulose filter being utilized as a standard or control.

' The actual quantity of gas is not reported but the peak 35 height of the gas chromatograph analysis is indicated,

which is proportional to concentration.

From the above data it can be seen that the porous glass filters are considerably more effective in reducing the amount of harmful gases such as acetaldehyde and acetone passing through the filter than is the standard cellulose filter. The porous glasses having small pores (Glasses 1a, 1e, and lg), that is, pores between about 100 angstroms and 500 angstroms appear more effective in removing gases such as acetaldehyde and acetone than does the glass having pores in the range of 750 to 1,000 angstroms (Glass 1 f). However, even the material having larger pores is more effective in removing gases than a standard cellulose filter.

None of the porous glass materials described in this example had been treated with water vapor, i.e., the hydroxyl concentration on the surface of the glass had not been altered from that which naturally exists on such glasses after phase separation, leaching, and washing.

EXAMPLE IV Porous glass material of the type described in Example I having a pore size of about 50 to 100 angstroms was compared with commercial filter for effectiveness in removing particulate matter from tobacco smoke. The porous glass filters were of a structure of the type shown in FIG. 3 wherein a 20 millimeter filter length consisted of 10 millimeters of cellulose acetate and a chamber 10 millimeters long containing porous glass.

The cigarettes tested were conditioned for 24 hours at 75F. and 60 percent relative humidity. Smoking was done in a room conditioned to 75 i2F. and 60 i2 percent relative humidity. The smoking system consisted of the cigarette, a tared Cambridge filtered assembly, and a smoking machine that produces a milliliter puff of 2 second duration at a rate of l puff per minute. All cigarettes were smoked to a butt length of 33 millimeters. Five cigarettes were smoked through Sample Acetaldehyde Acemne each Cambridge filter and the results calculated and Winston Cigarette with 20 mm recorded in terms of one cigarette. wStandarCd Cellulose lgilltgr 46 14 The table below reports total partlculate matter,

inston igarette Wlt mm Cellulose Film and [0 mm mo sture 1n particulate matter, n1c0t1ne, and tar. The Glass la 2s 7 molsture present in particulate matter was deterrmned w 10 mm according to a procedure described in a paper entitled Cellulose and 10 mm Porous I Glass 12 21 6 Determination of Molsture in Total Particulate Matwmsw" 10 mm ter by Schultz and Spears in Tobacco Science, Vol. X,

Cellulose and 10 mm Porous Glass lg 21 6 pp. -76 (I966), this descrlption bemg mcorporated Winston Cigarette with 10 mm herein by reference. The nicotine content was deterand 10 mm 35 mined by double distilling the particulate matter which Winston Cigarette with no 50 had been washed with dry dioxaneisopropanol :1 mm of any and reading in the ultraviolet in a spectrophotometer.

TABLE I Total Moisture in Particulate Particulate Nicotine Tar Cigarette Filter Matter (mg) Matter (mg) (mg) (mg) Winston None 41.2 5.4 L78 34.0 Winston Cellulose Acetate 30.5 3.9 l.47 25.2 Winston Porous Glass 26.9 2.8 1.28 22.9 Lark None 40.3 9.6 [.4 29.3 Lark Activated Charcoal 21.1 4.5 0.9 15.8 Lark Porous Glass 17, 4.0 0.8 12.7 Richmond None 3]. 8.2 1.3 2L5 Richmond Strickman Filter (9.2 in. draw) 9.5 2.8 0.5 6.3 Richmond Porous Glass 63 in. draw) 14.0 3.3 0.6 10.1

' 11 The tar cohtent was that which remained after sub trading the quantity of moisture and nicotine from the total particulate matter collected in the Cambridge filter.

In the above tests, the resistance'to air flow with the Winston cigarette with a commercial filter was about 4.1 inches of water while the Winston cigarette with the porous glass filter recorded 4.6 inches draw. The Lark cigarette with a commercial filter had a draw of about 5.3 inches while the Lark with a porous glass filter has a draw of about 5.0 inches; As indicated above, the Richmond filter had a draw of about 9.2 inches while the Richmond with a porous glass filter had a draw of about 6.3 inches. Although the Richmond commercial filter; that is, the Strickman filter, appears to be most efficient in removing particulate matter, it has the B 0 and 0.1 percent by weight Na O. The pore volume was between and percent. The surface area of the porous fibers was about 137 square meters per gram as determined by nitrogen absorption according to the method described by Emmett, Brunauer, and Teller in Journal of the American Chemical Society, 5 6, (1934) and 57, 1954 (1935). l

The effectiveness of these porous fibers as tobacco smoke filters was tested by preparing Winston cigarettes with a loosely-packed porous fiber glass filter element 20 millimeters in length. These cigarettes-were compared with a regular cellulose acetate filter and a non-porous fiber glass filter of fiber glass which had not been phase separated and leached. These filters were also 20 millimeters in length. The following table shows the results:

TABlIEll A P Average Particulate Matter Cigarette Filter Cm. of Water Puffs Passed Through Winston Cellulose Acetate 9.7 10 22.3 mg Winston Porous Fiber Glass 9.8 l0 16.4 mg Winston ***Regular Fiber Glass 9.7 10 17.3 mg Winston No Filter 4.0 10 35-36 mg The pressure drop shown is across the entire cigarette, including the filter.

Average of 10 cigarettes for each type of filter.

*"Regular, non-porous fiber glass of the same area of about 6 m /gm.

, highest resistance to draw and this is a distinct disad vantage. Also, the Strickmanmaterial does not exhibit gas absorption properties comparable to activated charcoal or porous glass.

EXAMPLE v Porous Fiber Glass Filter I Fibers were prepared having thefollowing calculated composition:

' Oxide Weight PenCent f Na,O 5 8,0, 20 75 Slo Raw materials for this glass were melted and fritted.

The fritted glass was then remelted at about 2,800F.

in a small crucible above a bushing having an orifice of about 6 microns diameter. The glass was held at about 2,800F. for about 1 hour before fibers were drawn. Fiber drawing conditions were a drawing speed of 5,000 feet per minute at a bushing temperature of 2,350F. during one run and a speed of 5,500 feet per minute at 2,410F. bushing temperature during another run. The fibers produced by both runs were substantially identical, having a diameter of about 6 microns. The fibers were cut into lengths of about 6 to 9 inches and spread out into a mat for heat treating. Heat treat- .and N. Ramasubramanian,

composition without phase separation and leaching has a surface The porous fiber glass proved to be significantly" non-porous fiber glass (non'porous) filter. Regular non-porous fiber glass has a nitrogen surface area of about 6 square meters per gram while the porous fiber glass utilized in this example had a nitrogen surface area of about 137 square meters per gram.

Fiber glass of potassia borosilicate performs in a manner to the soda borosilicate compositions described in this example.

Nitrogen surface areas of the microporous glass utilized in this invention were determined according to standard techniques. Such techniques are described by S. Brunauer in The Absorption of Gases and Vapors, Vol. I, p. 271, Oxford University Press, London (1945).

Method for determining the quantitative presence of hydroxyl groups on glass surfaces, especially porous glass surfaces, have been described by M. J. D. Low

Infrared Study of the Nature of Hydroxyl Groups on the Surface of Porous Glass, Journal of Physical Chemistry, Vol. 70, No. 9, pp. 2,740-2,746, September, 1966. The presence of hydroxyl groups on porous glass utilized in this invention was determined according to the techniques described by Low and Ramasurbramanian.

Techniques for determining components in cigarette smoke have been described by R. J. Phillippe, H. Moore, R. G. Honeycutt, and J. M. Ruth, Some Hydrocarbons of the Gas Phase of Cigarette Smoke,

Analytical Chemistry, Vol. 36, No. 4, pp. 859-865, April, 1964, and by R. J. Phillippe and M. E. Hobbs,

'So'me Components of the, Gas Phase of Cigarette Smoke, Analytical Chemistry, 2,0022,006, December, 1956.

Pore size reported hereinabove was determined by Vol. 28, No. 12, pp.

photographing a surface of the microporous glass i ough an electron microscope, physically measuring the pores on the photograph, and then dividing the measurement by the magnification of the microscope.

EXAMPLE VI present is not reported, but the peak height of the gas chromatograph analysis is indicated which is proportional to concentration.

Sample Acetaldehyde Acetone Winston Cigarette with 20 mm Standard Cellulose Filter 78 20 Winston Cigarette with 20 mm Porous Fiber Glass Filter 66 12 The porous fiber glass filter removed about 15 percent more acetaldehyde and about 40 percent more acetone than the cellulose acetate filter. V In vivo pulmonary dynamics and mucus flow bioassay, studies also illustrated the greater effectiveness of porous glass filters of this invention over cellulose acetate filters in elminating harmful ingredients present in tobacco smoke.

Pulmonary function determined by the method of. Mead, 1., Journal of Applied Physiology, 15, 325 (1960), as modified by Murphy, S. D., and Ulrich, C. E., American Ind. Hygiene Assoc., J., 25, 28 (1964) showed greater reduction of respiratory, tidal volume and minute volume when guinea pigs were exposed to smoke from a regular filter (cellulose acetate) Winston v cigarette than when exposed to smoke from a Winston cigarette having a porous glass filter of the type de- In mucus flow studies on young cats by the method of Goldhamer, R. E., Barnett, B., and Carson, S., Federation Proc., 23, 406 1964) the porous glass filters of the type described in Example HI proved considerably more effective than regular filter (cellulose acetate) when tested on Winston cigarettes. The least deviation from normal mucus flow is considered as least harmful to the specimen. The deviation from normal mucus flow was as follows:

Deviation Filter Regular filter Winston 58% Porous glass filter Winston 37% (Pores of about 900A) Porous glass filter Winston 35% (Pores of about 250A) The porous glass tobacco smoke filters of this invention proved extremely effective in removing tars, nicotine, and harmful gases from tobacco smoke. That this evidence was significant was demonstrated by pulmonary and mucus flow studies on live specimens.

While specific examples have been set forth hereinabove to illustrate the invention, the invention is not to be considered limited thereto, but to include all the variations and modifications falling within the scope of the appended claims.

We claim:

l. A method of increasing the smoke filtering activity of microporous glass comprising:

a. heating the microporous glass at a temperature on the order of to 600C. for about 5 to minutes in an atmosphere consisting essentially of water and an inert gas, thereby b. increasing the concentration of hydroxyl groups on the surface of the pores.

2. The method of claim 1 in which the temperature is in the range of 450 to 550C.

3. The method of claim 1 in which the inert gas is nitrogen.

4. The method of claim 3 in which the atmosphere contains on a volume basis:

a. lO-90 per cent water vapor, and

b. 90-10 per cent nitrogen. 

2. The method of claim 1 in which the temperature is in the range of 450* to 550*C.
 3. The method of claim 1 in which the inert gas is nitrogen.
 4. The method of claim 3 in which the atmosphere contains on a volume basis: a. 10-90 per cent water vapor, and b. 90-10 per cent nitrogen. 